Datasheet

LTC3428
8
3428fb
APPLICATIONS INFORMATION
Table 2. Capacitor Vendor Information
SUPPLIER PHONE FAX WEBSITE
AVX [phone] [phone] www.avxcorp.com
Sanyo [phone] [phone] www.sanyovideo.com
TDK [phone] [phone] www.component.tdk.com
Murata [phone] [phone] www.murata.com
Taiyo Yuden [phone] [phone] www.t-yuden.com
Output Diode Selection
For high effi ciency, a fast switching diode with low reverse
leakage and a low forward drop is required. Schottky diodes
are recommended for their low forward drop and fast
switching times. When selecting a diode, it is important to
remember that the average diode current in a boost
converter is equal to the average load current: I
D
= I
LOAD
When selecting a diode, make sure that the peak forward
current and average power dissipation ratings meet
the application requirements. See Table 3 for a list of
Schottky diode manufacturers. Example diodes are Philips
PMEG1020, PMEG2010, On-Semi MBRA210, IR 10BQ015,
Microsemi UPS120E, UPS315.
Table 3. Diode Vendor Information
SUPPLIER PHONE FAX WEBSITE
Philips [phone] www.philips.com
Microsemi [phone] [phone] www.microsemi.com
On-Semi [phone] www.microsemi.com
International
Rectifi er
[phone] [phone] www.irf.com
Thermal Considerations
To deliver maximum power, it is necessary to provide a
good thermal path to dissipate the heat generated within
the LTC3428’s package. The large thermal pad on the IC
underside can accomplish this requirement. Use multiple
PC board vias to conduct heat from the IC and to a copper
plane that has as much area as possible.
If the junction temperature gets too high, the LTC3428 will
stop all switching until the junction temperature drops
to safe levels. The typical over temperature threshold is
150°C.
Closing the Feedback Loop
The LTC3428 uses current mode control with internal,
adaptive slope compensation. Current mode control
eliminates the 2nd order pole in the loop response of voltage
mode converters due to the inductor and output capacitor,
simplifying it to a single pole response. The product of the
modulator control to output DC gain and the error amp
open-loop gain equals the DC gain of the system.
GG G
V
V
G
V
I
G
DC CONTROL EA
REF
OUT
CONTROL
IN
OUT
EA
=
=
≈
••
•2
100
The output fi lter pole is given by:
f
I
VC
Hz
POLE
OUT
OUT OUT
=
π ••
where C
OUT
is the output fi lter capacitor value. The output
fi lter zero is given by:
f
RC
Hz
ZERO
ESR OUT
=
1
2• • •π
where R
ESR
is the output capacitor equivalent series
resistance.
A complication of the boost converter topology is the right
half plane (RHP) zero and is given by:
f
VR
LV
Hz
RHP
IN O
O
=
2
2
2
•
•••π